Nephrotic Syndrome, characterized by massive proteinuria, hypoalbuminemia and edema, is one of the most frequently seen kidney diseases in children. Despite extensive research, the pathogenesis of this disease for the vast majority of cases remains unclear. Although glucocorticoids, the mainstay of therapy for over 50 years, are effective in most children, more than 20% develop steroid resistant nephrotic syndrome, placing them at significantly increased risk for the development of kidney failure. Despite its clinical importance, the molecular basis of steroid sensitive (SSNS) vs. steroid resistant nephrotic syndrome (SRNS) is unknown. Within the general population there is substantial, yet stable, interindividual variability in the clinical responsiveness to endogenous and therapeutic glucocorticoids. Although decreased responsiveness can have multiple origins, it is often caused by structural or functional abnormalities in the glucocorticoid receptor (GR). Such alterations can affect GR ligand affinity, receptor number or the ability to mount an appropriate transcriptional response. Moreover, altered expression of alternatively spliced isoforms of GR, as well as the frequency of certain polymorphisms, has been linked to clinical glucocorticoid hyporesponsiveness. Based on this knowledge, we hypothesize that alterations in GR structure and/or function are critical determinants of glucocorticoid resistance in childhood nephrotic syndrome By taking advantage of ongoing access to clinical samples and patient histories through a collaborative arrangement with both the Midwest Pediatric Nephrology Consortium and the ongoing NIH-sponsored FSGS clinical trial, we propose to analyze the mechanistic link between the clinical response to glucocorticoids and both the genetic structure as well as the biochemical and transcriptional properties of GR isoforms. Our specific aims are thus to: 1) Determine the expression of individual GR isoforms both at the protein and mRNA levels in lymphocytes isolated from children with SSNS vs. SRNS. 2) Comparatively analyze the functional properties of GR in the two populations by examining hormone binding activity as well as the transcriptional regulation of both glucocorticoid induced and repressed endogenous genes. 3) To examine the genomic sequence of the GR gene to determine whether clinical response is associated with specific genetic variants. By correlating the clinical response to glucocorticoid therapy to molecular markers of GR structure and function this project should provide not only a better understanding of the molecular basis of glucocorticoid responsiveness in nephrotic syndrome but also can form the basis to develop clinically applicable tools to more accurately guide therapeutic decisions in the treatment of this very common kidney disease. PUBLIC HEALTH RELEVANCE: Nephrotic Syndrome is one of the most common kidney diseases in children yet the underlying cause of this condition is largely unknown. Steroids are the main treatment for this disease. Although they are effective, more than 20% of children develop resistance to these drugs and this group is more likely to progress to more severe forms of the disease. This project aims to examine whether resistance is due to alterations in the cellular receptor for steroid drugs. Finding such an alteration would provide a better understanding of the reasons for resistance and allow physicians to identify which patients are likely to develop it. This knowledge would prevent unnecessary exposure to steroids for resistant children and would enable earlier treatment with other classes of drugs.